1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device having vertical gates.
2. Description of the Related Art
Recently, with high integration of semiconductor memory devices, sizes have shrunk and patterns have become fine. As the size of the device becomes smaller, a gate channel length is also reduced, causing operational speed or input/output rate of information to be slower due to current leakage caused by short channel effect, hot carrier effect and so on.
To prevent this phenomenon, vertical gates for securing a channel length have been proposed. Tungsten is used as the main material of gate in the conventional gate structures. However, for highly advanced semiconductor technology, tungsten which has great grain size is not suitable to be used as a gate material because tungsten presents higher resistance for vertical gates with reduced sizes. Therefore, there is a need to find a suitable material and fabrication process for vertical gate transistors.